Mobile phone technology is continually being improved to increase efficiency and reduce handset size, weight, and battery requirements. Reduced power consumption leads to smaller, lighter handsets with longer talk times. Increased efficiency is necessary for increased battery lifetime, as well as to support the ever-increasing features designed into mobile phones. Features such as MP3 players, FM radio, video players, and even televisions are being integrated into portable handsets. A common aspect of all these features is audio, thus requiring high quality audio amplification with minimal power usage. In addition to the RF amplifier circuit, one of the main power usage components in mobile phone handsets is the audio amplifier circuitry.
The audio output requirements of a mobile phone handset include a powerful polyphonic ring tone, natural and clear voice reproduction, and clean, noise-free music reproduction, either through headphones or earphones, or over the hand set built-in speaker. Thus, the system may be capable of delivering high output power for built-in speaker operation, lower power but high quality audio output for voice or music playback, and low power consumption when idle. Even when no input signal is present, such as in a lull in conversation, there is still significant power usage by the audio circuits. One technique to reduce power usage is to shut down audio amplifiers when no input signal is present. Another is to improve the efficiency of the amplifier.
Primary factors in audio amplifier performance include frequency response, gain, noise, and distortion. While it is highly advantageous to increase battery lifetime, it must be accomplished without sacrificing audio signal output quality, i.e. maintaining high gain while suppressing noise and distortion.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.